Thiocyanate Determination using Technique of Flow Injection-Gas Diffusion Spectrophotometry with Cerium(IV)-Ninhydrin Reagent

摘要

Numerous food plants contain thiocyanate, which can inhibit iodine uptake of thyroid gland and induce to the risk of iodine deficiency disorders(IDD).This research is focused on the development of new method for thiocyanate determination based on the formation of red hydrindantin using spectrophotometric flow injection(Fl)-gas diffusion technique.In this technique, thiocyanate is oxidized by cerium(IV)in the acid donor stream to form hydrogen cyanide which diffuses through the membrane in the gas diffusion cell and reacts selectively with alkaline ninhydrin in the acceptor stream to form a red hydrindantin detected by spectrophotometer at 485 nm.The common operational conditions including sample volume, the length of mixing coil, and the flow rate as well as chemical parameters(concentration of cerium(IV)and ninhydrin, and pH reaction)were optimized with respect to sensitivity, analysis time, and linearity.The optimum condition notified by highest absorbance with sharp single peak and fast analysis was obtained under flow rate of 2 mL min~(-1), 300 pL sample volume, 75 cm mixing coil, 0.01 M cerium(IV), 1 % ninhydrin, and pH of 11.The interfering ions frequently exist with thiocyanate were also studied.Under the optimized conditions, the method showed linear for thiocyanate concentration from 5-30 mgL~(-1)and sampling rate of 120 s/h with a satisfactory reproducibility(RSD < 2% at n=3).This method has been successfully applied to determine thiocyanate in saliva from smoker and non-smoker and the results showed good agreement with those obtained from standard spectrophotometry method.